Standardization works of international mobile telecommunication (IMT)-advanced which is a next generation (i.e., post 3rd generation) mobile communication system are carried out in the international telecommunication union radio communication sector (ITU-R). The IMT-advanced aims at support of an Internet protocol (IP)-based multimedia service with a data transfer rate of 1 Gbps in a stationary or slowly moving state or 100 Mbps in a fast moving state.
Long term evolution-advanced (LTE-A) of 3rd generation partnership project (3GPP) is one of promising candidates of a system standard satisfying requirements of the IMT-advanced. The LTE-A is an improved version of 3GPP LTE (hereinafter LTE). The LTE is a part of evolved-UMTS (E-UMTS) using evolved-universal terrestrial radio access network (E-UTRAN). The LTE employs orthogonal frequency division multiple access (OFDMA) in a downlink and employs single carrier-frequency division multiple access (SC-FDMA) in an uplink.
A 3GPP LTE system uses hybrid automatic repeat request (HARQ) to increase transmission efficiency. The HARQ can be classified into downlink HARQ and uplink HARQ. In the downlink HARQ, when a base station (BS) transmits downlink data, a user equipment (UE) transmits an acknowledgement (ACK)/not-acknowledgement (NACK) signal for the downlink data. In the uplink HARQ, when the UE transmits uplink data, the BS transmits an ACK/NACK signal for the uplink data.
In a case where HARQ is applied in general to the LTE or other wireless communication systems, an HARQ timing relationship is defined with a channel of 8 transmission time intervals (TTIs), that is, an HARQ period corresponding to an interval of 8 subframes. The HARQ timing relationship shows a time-domain relation for a transmission start time of an ACK/NACK signal for reception data and a retransmission start time of data in case of receiving the NACK signal. The HARQ timing relationship is determined by considering a decoding time of shared channel data and the ACK/NACK signal on the uplink or the downlink.
However, a future wireless communication system such as LTE-A may require to change the conventional HARQ timing relationship. For example, a required HARQ period may be decreased due to diversification of UE capability and due to decrease in a decoding processing time of the BS and the UE. Alternatively, the required HARQ period may be increased since a relay station and a new technique such as multiple input multiple output (MIMO) using a greater number of antennas are applied to the future wireless communication system. Therefore, there may be a case where a heterogeneous HARQ timing relationship has to be applied in the wireless communication system.
Accordingly, there is a need to consider how to perform an HARQ process having a heterogeneous HARQ timing relationships and how to perform signaling and radio resource allocation when performing the HARQ process in the wireless communication system.